A) Field of the Invention
The present invention relates to a superconductive filter and a filter characteristic adjusting method, and more particularly to a superconductive filter and a filter characteristic adjusting method, capable of changing a filter bandwidth without changing the shape of resonator patterns formed on a dielectric substrate.
B) Description of the Related Art
A recent spread of mobile phones has made it essential to use high speed and large capacity transmission technologies. A superconductor has a very small surface resistance even in a high frequency area, as compared to a general electric conductor. Therefore, the superconductor is suitable for the material of a conductive pattern of a planar circuit type filter. The discovery of high temperature oxide superconductors and the development of refrigerators have greatly mitigated an issue of cooling a superconductor.
JP-A-HEI-10-209722 discloses a technique of adjusting impedance by forming a dielectric film on a strip line made of superconductive material or trimming a width of the strip line. JP-A-2004-64359 discloses a technique of changing a filter band-pass characteristic by controlling temperature of a superconductive filter. JP-A-2005-354657 discloses a technique of adjusting a filter characteristic by moving up or down an adjustment plate made of a normal conductor or a superconductor and disposed above a superconductive filter pattern.
JP-A-2002-204102 discloses a technique of adjusting a filter characteristic by moving up or down a dielectric plate disposed above a superconductive filter pattern by using a piezoelectric actuator. A superconductive filter disclosed in JP-A-2002-57506 is constituted of a plurality of half wavelength hair pin type patterns disposed along a straight line generally at an equal pitch. Each hair pin type pattern is slid transversally by a piezoelectric actuator to adjust a coupling coefficient of respective stages.